Production of staple fibers



Feb. 12, 1963 s. lBRAHlM I 3, 7 ,006

PRODUCTION OF STAPLE FIBERS Filed Oct. 30. 1961 INVENTOR SALIM M. IBRAHIM ATTORNEY United States Patent This invention relates to a method for preparing blends of staple fibers from continuous elastic filaments and inelastic laments. More particularly, this invention relates to a method for converting continuous elastic filaments and inelastic filaments into staple fiber which may be processed into slivers of intermingled elastic and inelastic staple fibers which may be subsequently processed into high quality stretchable yarns and stretchable fabrics by utilizing known processing equipment.

ethods for preparing blended sliver from two or more different kinds of inelastic continuous filaments are well known. However, the application of these methods to the preparation of blended sliver from continuous elastic filaments and inelastic filaments has not proved to be satisfactory. After cutting the elastic fibers to staple lengths, they tend to remain in tightly formed clumps that resist separation in the blending with inelastic staple fibers and cause such crinkling and wrinkling of the fiber sheet as to render it totally unprocessable.

it is, therefore, an object of this invention to provide an improved method for preparing blends of staple fibers from continuous elastic filaments and inelastic filaments. It is another object of this invention to provide a method for preparing blended sliver from continuous elastic fil ments and inelastic filaments which permits the use of conventional equipment for converting such filaments into sliver form. A further object of this invention is to provide a method whereby continuous elastic filaments and inelastic filaments are simultaneously cut to staple lengths whereby the elastic fibers have a high degree of length uniformity. Other objects will be apparent hereinafter.

The objects of this invention are achieved by a method which comprises first forming a plurality of separated flat sheets of continuous elastic filaments and inelastic filaments. The sheets of elastic filaments are tcnsioned to stretch the filaments a predetermined amount beyond their normal relaxed length. After the tensioning step, the elastic filaments are combined in layered relationship with the inelastic filaments to form a composite web in which the sheets of tensioned elastic filaments lie between adjacent sheets of inelastic filaments. Without permitting the elastic filaments to retract, the composite web is fed to fracturing means where the filaments are cut to staple length. Surprisingly, the elastic staple fibers thus prepared are found to be of uniform length, and the blend of elastic and inelastic fibers exhibits excellent processability in the subsequent steps of converting the fibers to sliver and ultimately to yarn form.

By the term elastic filaments and fibers" it is meant synthetic and natural filaments and fibers having a high brealdng elongation, e.g., 109% or more and preferably 5 00% to 800%, and a low elastic or initial modulus, e.g., less than one gram per denier, preferably 0.08 gram per denier or lower, and exhibit a quick and substantially complete recovery from stretching to an amount less than their breaking elongation, e.g., have a tensile recovery of about 90% or more and a stress decay of less than about 20%.

By the term inelastic filaments and fibers it is meant those natural and synthetic fibers which generally have a breaking elongation of less than about 100% and, as compared to the elastic fibers, have a relatively high elassenses "ice tie or initial modulus, e.g., from 4 to grams per denier or greater.

The invention will be more fully understood by reference to the accompanying drawing in which the fig ore is a side view of a schematic representation of apparatus for converting the filaments to staple fibers.

Referring now to the figure, reference letters A and A represent fiat sheets or tows of inelastic filaments and reference letter B represents a flat sheet of continuous elastic filaments. The inelastic filaments A are passed over tension bars til, 12, id, and to to a pair of input feed rolls 33 and at Simultaneously the elastic filaments E are passed over a tension bar 13, between two pairs of feed rolls 2fi-22 and 26-23- and forwarded in a stretched condition to the input feed rolls 38 and so. At the same time, inelastic filaments A are passed over tension bars 3th 3-2, 34- and 36 to the input feed rolls 33 and 4th in delivering the elastic filaments E to the input feed rolls 3t and 4d, a predetermined amount of stretch is imparted to the filaments by driving feed rolls 262% at a higher linear surface speed than feed rolls 2tl--22. This stretch is maintained by input feed rolls 38 and it), at which point the sheets of inelastic filaments A and A are combined into a composite web with the sheet of elastic filaments E. The composite web is forwarded by the input feed rolls 38 and so to fracturing rolls 42. and 44 where the continuous filaments are cut to staple fiber length. The staple fibers are picked up by pick-up rolls 45 and 43 and may be forwarded directly to a suitable container 52 as cut fiber or processed to sliver form S by suit-able apparatus Eli.

As previously indicated, the stretching of elastic filaments B may be accomplished by driving feed rolls 2 fi2fi at a higher linear surface speed than feed rolls Edi-22. Unless some appreciable stretch, e.g., at least about 2%, is imparted to the elastic filaments, the cut bers tend to form tight clumps that resist distribution in the blend and cause such severe crinkling and wrinkling in the cut fiber sheet as to make it totally unprocessable. Generally it is preferred that the elastic filaments E be stretched an amount from about 5% to about 15% greater than their relaxed length; however, it has been found that little advantage is gained in processability or cut length uniformity at stretch levels much above 15%.

Some tension should also be applied to the inelastic filaments. This tension should, of course, be sufficient to maintain a uniformly flat sheet. Tensions which stretch or deform the inelastic filaments should generally be avoided.

in practicing the present invention, particularly desirable results have been obtained by flexing the elastic filamerits E before formation of the composite web, e.g., as they pass between the two sets of feed rolls during the tensioning step. Referring again to the figure, an oscillating roll 24 may be positioned between the two sets of feed rolls 243-22 and 26-2 3 to stretch the elastic filaments from about 2 to about 5 times, preferably about 3.5 times, their relaxed length during the tension step. Alternatively, the elastic filaments may be flexed before entering the stretching zone. One cycle of stretching and relaxing is generally all this required; however, additional cycles may be used. It is, of course, necessary in all cases that the elastic filaments be in the previously described stretched condition of from about 2% to about 15% and sandwiched between layers of inelastic fibers when fed to the fracturing rolls.

After fracturing the filaments, the staple fibers may, as previously indicated, he directed into a suitable receptacle or preferably processed immediately into top, sliver, batts,

ya as, fabrics, and other textile forms using conventional processing machinery. The fracturing step with the subsequent steps of aligning the fibers to form a web and drafting the web and rolling the drafted staple fibers into a helical roll or sliver are conveniently achieved using equipment described in U.S. 2,438,469, which is commonly known as the Pacific Converter. The equipment described in U.S. 2,748,426, known as the Turbo Stapler, may also be used. Because of the significant difierence in break elongations of the elastic and inelastic fibers in the composite web, less satisfactory results are achieved on systems which depend on breaking the fibers by stretching rather than fracturing. Other apparatus such as the variable cutter attachment for the Pacific Converter described in U.S. 2,599,148 may be utilized. Most advantageous results are obtained when the elastic fiber component is cut to uniform lengths which are relatively long, '.e., from about 3.0 to 6.0 inches, although both longer and shorter lengths may be prepared by the method described herein. If it is desired to utilize inelastic filaments of significantly shorter lengths, it is within the scope of the present invention to utilize, as the sheet of inelastic filaments, natural or synthetic staple fibers in sliver or web form.

From a practical viewpoint, the commercially available apparatus for converting continuous filaments directly to sliver, i.e., the tow-to-top conversion systems widely used in the textile industry, are designed to operate on tow bundles of 1.5 to 2 million total denier. In addition, the inelastic fibers are commercially available in tows of from 200,000 to 500,000 total denier. Since it is a requirement of the present invention that the elastic filarnents be sandwiched between the layers of inelastic fibers, the inelastic fibers will generally account for a minimum of one-half to one million denier or approximately onefourth to one-half the capacity of the conventional apparatus. Thus, from a practical standpoint, the elastic filament content of the composite tow will have as its upper limit approximately 50 %to 80% of the total fiber weight. Preferably, the elastic filaments will comprise from about 3% to about 50% of the composite tow or web. It is to be understood, however, that as little as about 1% of the total weight may be provided by the elastic filaments.

The following examples, in which parts and percentages are by weight unless otherwise indicated, further illustrate the present invention. In the examples, the term elongation when applied to yarns refers to the total yarn stretch attributable to the elastic fiber component and is the ratio of the extended length of the yarn to its original length expressed as percent of the original length. The term power is a measure of the resistance to stretch of the yarn expressed in grams per denier and is measured at selected points based on the extended length specified.

EYAMPLE I ,(a) Preparation Elastic Filaments Into a reverse centrifugal mixer maintained at 50 C. are fed a stream of polytetrarnethylene ether glycol at a rate of 8 pounds per hour and a stream of liquid p,p-methylenediphenyl diisocyanate at 2 pounds per hour. The polytetramethylene ether glycol has a molecular weight of about 2,000 and is thoroughly pre-dried by treatment with a molecular sieve. The reagents are intimately mixed, and are discharged continuously into a jacketed pipeline maintained at about 96 C. and extending for 25 feet. The pipeline serves as a reactor in which the polyether glycol is capped wit-h 2 mols of the diisocyanate to yield an isocyanate-terminated polyether. The average time spent in the pipeline reactor is between 90 and 100 minutes. On emerging from the pipeline reactor, the isocyan'ate-terminated polyether is cooled at once to below 45 C. The cooled isocyanate-terminated polyether is conducted at a rate of, 9.2 pounds per hour into a highshear mixer containing a rotating disc, and a stream of N,N-dimethylformarnide is added at 42.8 pounds per hour. The mixture (17.7% solids) is thoroughly agitated for 4 minutes and then passes to a chamber in which a mixture of hydrazine (35% in water) and diethylamine (5% in dimethylformamide) in the ratio of 37.5 parts of hydrazine to 1 part of diethylamine is added as a single stream at a rate of 0.465 pound per hour with strong agitation. The mixture passes to a reaction chamber held at a tem' perature of 2040 C., the contents having residence time of about 2-3 minutes. The emerging polymer solution contains approximately 17.7% solids and has a viscosity of 700 poises at 30 C. To the polymer solution are added a slurry of titanium dioxide in dimethylformamide a solution of poly(N,N-diethyl-beta-aminoethyl methacrylate) in dimethylformamide and a solution of 4,4'-butylidenebis-(6-t-butyl-m cresol) in dimethylfiormamide, such that the final mixture contains 5%, 5%, and 1%, respectively, of each additive based on the polyurethane.

This solution is then extruded through a 960-l1ole spinneret (orifice diameter 0.0025 inch) into an aqueous bath containing 50% dirnethylformamide and 5-1 0% talc, and maintained at about 95 C. The 6,000-denier tow thus formed is removed at about 40-50 yards per minute and passed through a water bath maintained at C. to C. until the filaments contain less than 0.5% dirnethylformamide. After application of a talc finish, the tow is dried in a relaxed condition for three hours at 104 C. and then heated for 45 minutes at C. The spandex tow thus produced has an individual filament denier of 6 and total tow denier of approximately 6,000.

(12) Preparation of Composite Tow The spandex tow is used to prepare a composite tow comprising about 10% by Weight of the spandex tow and about 90% by Weight of a commercially available inelastic acrylonitrile polymer fiber tow. The inelastic tow has a filament denier of 3 and a total tow denier of 470,000. Referring to the apparatus illustrated in the drawing, one end of the inelastic tow is spread out to form a wide sheet A and two ends of inelastic tow are spread similarly to form wide sheets and superposed in two layers to form sheet A. Twenty-four ends of the spandex tow are disposed over the same width to form sheet E. The tension on the spandex tow E is so regulated that the spandex filaments are under a stretch of 5% to 10% as they are sandwiched between the layers of inelastic tow and enter between input rolls 38 and 40 which are, in this case, the input rolls of a Pacific Converter described in U.S. 2,438,469.

(0) Preparation of Staple Fiber Staple fiber samples are cut from the composite tow on the Pacific Converter to lengths of 3", 4%", and 6". No finish is applied to the composite tow during processing. Staple length measurements are made on both the spandex and inelastic fibers after cutting and the standard deviation (3) and coefiicient of variation (CV) are calculated according to conventional statistical procedure. The results are set forth in Table 1, which follows.

TABLE 1 Inelastic fiber S d v Nominal cut length, pan ex (elasm) fiber inches Avg. 0 CV, Avg. a- C",

percent percent Surprisingly, as seen from Table 1, the cut length of the spandex fiber is very close to the desired nominal length for which the Pacific Converter was set, and the length distribution is unusually uniform. It is particularly surprising that the spandex fiber shows a greater accuracy of average cut length and a more uniform distribution of cut lengths than does the inelastic fiber.

Cutting performance and subsequent processability to sliver on the Pacific Converter are observed to be excel lent, free of roll wrapping and tangling. The sliver obtained is then spun into yarn using conventional equipment and procedures for pin drafting, roving, and spinning. Samples of each of the three fiber cut lengths are spun to 238% and the power is .073, .12 and .233 gram per denier at 60, 75 and 90% of the extended yarn length, respectively. Processability and yarn properties are not afiected adversely by the use of the low filament denier for the 20/1 cc. yarn with a twist of 13.4 2. The power and inelastic fiber. elongation values of the yarn, as previously defined, are EXAMPLE lV e f l Set form m Tabla Whlch Four ends of the inelastic tow of Example I and 35 TABLE 2 ends of the spandex tow of Example I are combined by the process of Example I and FlGURE l to form a com- POWQY wrung/0611ier posits tow having a composition of 90% inelastic fiber at indicated percent Yarn 1 1 i v Spandex fibers nominal cut length, of extended yarn elqngaf lgfifidfili filJBI'. 0116 part Of this Composite tow n lengm is processed on the Pacific Converter with a 3 /2 variable percent cut and the remainder is processed Wlth a 6 straight out. 60% 75% 99% Each portion is then further processed as in Example I to a /1 cc. yarn with 13.4 t.p.i. Z twist. The data in H table 4 below show that the fiber length of the spandex .001 .100 .10 251 fiber is surprisingly close to the nominal cut lnegth in each instance and the yarn property data in Table 4 again X pp H 20 illustrate the desirable level of yarn properties attainable 1 throueh th use of the recess of this invention. The spandex tow and the inelastic t w or Example I are L m P T used to prepare a group of composite tows of different fiber blend ratios, generally following the procedure indicated schematically in the FlGURE of the drawing. The cut'lengm number of ends 01 the two tows are varied as necessary 1 v b1 h to produce the desired blend ratios. in all cases, the 34 e 6 ends of spandex tow under 5% to 10% stretch are sand- Yb 1 t1 4- a wicned between layers of the inelastic tow. When more 1 fi ig t fg inches 27 52 than one end of inelastic tow is used as either A or A in 1:8; 851; the FIGURE, they are disposed as superimposed, wide 30 h2$g1gg5gggg1 3 3 sueets as in Example 1. Each composite tow sample is i fig processed on the Pacific Converter to a 4 /2 variable cut, Yam fg g and subsequentlv processed as in Example I to a 20/1 POWQPiHgFamS/denler mindicsledpercenl F L of extended yarn1engtl1 cc. yarn with 13.4 t.p.1. Z twist. F1001 len th distribution 60%" 2 in the Pacific Converter sliver is determined for each 1 L 0 sample and is reported in lable 3. nisn ahon, percent 202 274 it will be noted that the cut length distribution of the spandex fibers is surprisingly good and again superior to EXAMPLE V that of the inelastic fibers although not so markedly superior as we'e the straight out samples of Example I Thflty-five ends of the spafldeX low of Example 1 are shown in Table 1. It will further be noticed that this mbmcd with four ends of a commercially available excellent cutting performance is achieved over the entire polyethylene terephthalate tow having a total tow denier range of blend levels represented in these samples. Data of 450,000 and an individual filament denier of 2.25. on the power and elongation of the yarns spun from the The composite tow formed by the process of Example I several composite tows are also given in Table 3. has a fiber composition of 90% polyethylene terephthalate TABLE 3 Cut length, inches Power in grams] Ccrnpositetow, denler 111 denier at indicated Yarn Spandex m1 ons percent ofexelonga- Sample content, Inelastic fiber Spandex fiber tended yarnlength tiou,

percent percent Total Spandex Inelastic Aver- 0' CV, Aver- 0' CV, 75% 90% age perage percent cent as 1. 401 .054 1.410 007 .141 .311 124 10.0 2.000 .210 1. 820 4.51 .30 s. 73 4.07 .27 0.03 .073 .122 .240 272 13.0 2.100 .300 1.800 4.35 .33 7.47 3.72 .10 4.30 .007 .100 .200 204 17.0 1.710 .300 1.410 4. 47 .30 3.70 4. 09 .31 7.03 .000 .102 .100 277 17.0 2.230 .400 1.000 4.59 .27 5.05 3. .23 0.00 .005 .104 .193 201 21.0 2.300 .500 1.000 4. 48 .23 5.03 4.44 .10 4.00 .003 .000 .173 273 22.0 1.010 .400 1.410 4.47 .20 0.50 4.47 .22 5.01 .004 .101 .100 283 20.2 1. 010 .500 1. 410 4.30 .37 s. 70 4.00 .10 4.02 .002 .000 .175 274 30.0 2.010 .000 1.410 4. 27 .20 0. 02 4.13 .13 4. 33 .050 .002 .101 207 EXAMFLE III In this example, the inelastic tow of Example I is re- 05 placed by another inelastic tow of the same composition and total tow denier but having an individual filament denier of 2. Three ends of this tow are combined with 35 ends of the spandex tow of Example I by the procedure outlined in Example I to form a composite tow comprising 87% inelastic fiber and 13% spandex fiber. The composite tow is processed on the Pacific Converter with a 4 /2" straight cut and is subsequently spun to a 42/2 cc. yarn with 22.8 t.p.i. Z. twist in the singles and 22.8 t.p.i. S twist in the ply. The elongation of the ply yarn is fiber and 10% spandex fiber. The spandex fibers under 5.40% stretch are sandwiched between layers or" the polyethylene terephthalate fibers. The composite tow is processed on the Pacific Converter with excellent processebility and performance.

in the same manner as in Example I, thirty-seven ends of the spandex tow of Example I are combined with three ends of the polyethylene terephthalate tow of the present example. The composite tow, comprising 86% polyethylene terephthalate fiber and 14% spandex fiber, is processed on the Pacific Converter to 3%." variable cut. Staple length measurements made on fiber samples taken 7 from the Pacific Converter sliver again show better cut length uniformity for the spandex fiber than for the inelastic fiber as indicated in Table 5.

Six ends of the spandex tow of Example I are passed to a pair of driven rolls and thence to a second pair of rolls driven at a linear surface speed 3.3 times that of the first pair of rolls so that the spandex tow is stretched 3.3 times in passing between the two sets of rolls. The stretched tow is then wound on a spool motor-driven at a speed such that the tow is wound in a relaxed condition. Thirty-eight ends of this previously stretched and relaxed tow are restretched to -10% stretch and then combined under this stretch with 3 ends of the inelastic tow of Example III by the procedure of Example I to form a composite tow comprising 86% inelastic fiber and 14% spandex fiber. The composite tow is processed on the Pacific Converter with a 4 /2" variable cut. The Pacific Converters sliver is given 6 passes of pin drafting. Another composite tow is prepared and processed in an identical manner except that the spandex fiber is not stretched and relaxed before incorporation under 5-l0% stretch in the composite tow. Sliver from the final pin drafting operation for each sample is examined for neps and unseparated clumps of fibers. The results shown in Table 6 clearly show the improvement obtained by the stretching and relaxing pre-treatment of the spandex tow.

EXAMPLE VII One end of the inelastic tow of Example I is passed through a Turbo Stapler as described in US. 2,748,426. At the same time, three ends of the spandex tow of Example I are fed to the Turbo Stapler so that they bypass the heating and drawing zone and are folded into the inelastic tow at the rolls commonly known as the intermediate rolls. As they enter the intermediate rolls and are combined with the inelastic tow, the spandex tows are under a stretch of about 50%, and still further stretch is applied as the combined tows pass to the breaker bars. Staple length measurements on fibers taken from the Turbo Stapler sliver show more uniform staple lengths for the spandex fiber than for the inelastic fiber, as shown in Table 7.

EXAMPLE VIII Three ends of the inelastic tow of Example I and four ends of spandex t-ow identical to that of Example I except having a total denier of 40,000 are combined as in 5 Example I to form a composite tow comprising inelastic fiber and 10% spandex fiber. The composite tow is cut on the Pacific Converter to 4 /2" variable cut. The spandex tow is given varying amounts of stretch as it is combined with the inelastic tow at the input rolls of the Pacific Converter, as shown in Table 8. From the staple length data obtained on fiber samples from the Pacific Converter slivers, it will be noted that the principal effect of increasing the stretch is to decrease the staple length of the spandex fibers.

TABLE 8 Spandex fiber length Percent stretch Avg, a CV,

inches Percent It will be apparent to those skilled in the art that any of a great number of elastic and inelastic natural and synthetic fibers, as well as fiber blends, may be substituted for those specifically disclosed in the foregoing examples. Among the many inelastic fibers are those prepared from the synthetic fiber-forming materials such as polyesters, e.g., polyethylene terephthalate; polyamides, e.g., polyhexamethylene adipamide, polyhexamethylene sebacamide, polycaproamide, and copolymers of various amides; acrylic polymers and copolymers, e.g., polyacrylonitrile, copolymers of acrylonitrile with vinyl chloride, vinylidene cyanide, vinyl pyridine, methyl acrylate; vinyl polymers, e.g., vinyl chloride/vinyl acetate copolymers; polymers and copolymers of tetrafluoroethylene, monochlorotrifiuoroethylene, and hexafiuoropropylene; polyethylene; cellulose derivatives, e.g., cellulose acetate, regenerated cellulose, ethyl cellulose, cellulose triacetate; glass, or from any natural fibers, such as cotton, wool, silk, jute, linen, or a blend of two or more inelastic fibers.

A particularly suitable class of elastic fibers for use in this invention are the spandex fibers. Among the segmented polyurethanes of the spandex type are those described in several patents, among which are US. Patents 2,929,800, 2,929,801, 2,929,802, 2,929,804, 2,953,839, 2,957,852, and Re. 24,689. As described in the aforementioned patents, the segmented polyurethane elastomers are comprised of amorphous segments derived from polymers having a melting point below about 50 C. and a molecular weight above about 600, and contain from about 5% to 40% of crystalline segments derived from a polymer having a melting point above about 200 C. in the fiber-forming molecular weight range. Most of suchpolyurethanes, when in filament form, have elongation greater than tensile recovery of over 90%, and a stress decay of less than 20% as defined in U.S. 2,957,852.

Fibers of other types of condensation elastomers are also suitable. US. 2,670,267 describes N-alkyl-substituted copolyamides which are highly elastic and have a suitable low modulus. A copolyamide of this type, obtained by reacting adipic acid with a mixture of hexamethylenediamine, N isobutylhexamethylenediamine, and N,N'-isobutylhexamethylenediamine, produces an elastomer which is particularly satisfactory for the purposes of this invention. US. 2,623,033 describes linear elastic copolyesters prepared by reacting glycols with a mixture of aromatic and acyclic dicarboxylic acids. Copolymers prepared from ethylene glycol, terephthalic acid, and sebacic acid have been found to be particularly use ful. Another class of useful condensation elastomers is described in US. 2,430,860. The elastic polyamides of this patent are produced by reacting polycarbonamides with formaldehyde.

Elastic fibers of textile denier from fiber-forming addi tion polymers such as, for example, copolymer of butadiene/styrene, butadiene/acrylonitrile and butadiene/Z- vinyl pyridine, polychlorobutadiene, copolymers of isobutylene with small proportions of butadiene, chlorosulfonated polyethylene, copolymers of monochlorotrifluoroethylene with vinylidene fluoride, and the like, may be employed.

Both the elastic and inelastic filaments may be supplied on packages of any convenient and available form. They may be in the form of individual filaments, or of relatively small bundles of filaments of low total denier, e.g., 200 to 1,000, or as tows or" high total denier of the order of 400,000. While the rawing shows a three-layered composite tow structure, it is to be understood that other structures are within the scope of the invention provided that the elastic fibers are sandwiched between at least two layers of inelastic fibers. The choice of alternate arrangements will depend on the equipment to be used and the form in which the starting yarns is supplied.

The slivers made by the process of this invention can be used in the manufacture of yarns suitable for use in elastic or stretchy woven, knitted, and non-woven fabrics for use in universal fitting apparel (socks, polo shirts, underwear, bathing suits, gloves, elastic cuffs, sweaters, waistbands, suits, coats, dresses, skirts, action sportswear, leotard-type outer wear, and ac essories such as tapes, webbings, and other woven, non-woven, or knit apparel fabrics), household products (form-fitting upholstery, slipcovers, sheets, carpets, mattress coverings, and narrow tapes and webbings for a Wide variety of uses), industrial products (transportation upholstery, woven and nonwoven felts, tapes and Webbings for varied applications), and medical products (surgical bandages, supports, elastic dressings, surgical stockings, and splint tapes). in addition, low stretch, high recovery fabrics can be made suitable for use in outer apparel (sweaters, knit jersey, and woven, knit, or non-woven suitings and dress goods), household items (rugs, carpets and upholstery), and industrial products (Woven, non-woven, and knit compression or impact-bearing structures). Illustrations of various specific products which may be prepared from the fiber blends and yarns made by the process of this invention are shoe laces, shoe liner fabric, shoe upper fabrics, house slippers, skin diving suits, snow suits, ski pants, football pants, slacks, llannels, sport shirts, bulky knit sweaters, blankets, swimming pool covers, toupee bases, belts, suspenders, garters, watch bands, ropes, elastic sewing thread, shock cords, bookcover jackets, bookbinding cloth, synthetic paper, elastomer-coated fabrics, and super-dense felts, such as papermakers felts.

The fiber blends, yarns, fabrics, and other textile products prepared from the slivers made by this invention may be given the customary finishing treatments where necessary or desired, such as scouring, Washing, drying, pressing, dyeing, heat-treating, and softening.

With particular reference to dyeing, good union dyeings of excellent lightfastness can be achieved on blends of spandex fibers with cotton in a one-bath procedure. Vat dyes of the anthraquinone type are used under essentially conventional vat dyeing conditions except that the alkalinity of the dye bath is reduced.

It is Well known to convert vat dyes by strong reducing agents, such as sodium hydrosulfite, to the sodium salt or basic leuco forms under conditions of relatively high alkalinity, e.g., 8 g. NaOl-l/liter. Excellent fastness properties result When cotton is dyed under these conditions. The spandex fibers show very low afilnity for the basic leuco form of vat dyes. Under appropriate and wellknown conditions, the dyes can be converted two further steps, first to the half sodium salt or half acid form, and second to the dihydroxy derivative or acid leuco form.

This last form shows good aifinity for spandex fibers but no affinity for cotton.

It has now been found that one-bath unions of cotton and spandex fibers can be obtained by adjusting the alkalinity of the vat dye bath to a point where there is equilibrium between the sodium salt (basic leuco form) and the half acid. In this one-bath method, the vat dye is reduced in the usual manner with sodium hydrosulfite, but with only about half the usual amount. of alkali in the bath. The exact amount of alkali to be used will vary somewhat with the vat dye being used, and can be readily determined by those skilled in this art. The alkalinity of vat dye baths for cotton is commonly equivalcut to about 8 g. NaOH/liter. Optimum alkalinities for union dyeing of cotton/ spandex blends with several representative dyes are shown in the following table. Identification of the dyes is according to the Technical Manual of the American Association of Textile Chemists and Colorists, 1960 edition, page 308. The C1. references are to the Colour Index, second edition, 1956.

At the optimum alkalinities of Table 9, the shades produced on the cotton and on the spandex fiber are equivalent, that is, good unions are achieved. When the desired shade has been obtained, the leuco forms are then oxidized according to conventional practice for vat dyes, e.g., with sodium perborate. Union dyeing of cotton/spandex blends made by this modified one-bath procedure with the vat dyes listed in Table 9 and similar dyes exhibit lightfastness in excess of 40 hours and good washfastness.

The process of this invention makes possible the production of new and useful elastic yarns making more efficient use of the elastic fiber content than is obtained by the conventional cut staple fiber route. The use of the composite tow eliminates the limitations on denier and length resulting from formation of neps and high fiber breakage during carding. The use of longer staple fiber lengths for the elastic fiber content reduces the number of free fiber ends in the yarn bundle and is advantageous in improving such yarn and fabric performancy characteristics as fuzzing, pilling, hand, color change, and dyeability. As illustrated in the examples, the use of longer fiber lengths results in more efilcient use of the elastic fiber component as reflected in the values for yarn power. Improved recovery of yarns and fabrics is a direct consequence because of the increased power available to overcome friction caused by fabric or yarn geometry. it is particularly surprising and unexpected that a fiber of elastic characteristics can be cut to uniform fiber length when incorporated under tension in a composite tow.

As many Widely difierent embodiments of this invention may be made Without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. In the method of producing a blend of separate out lengths of elastic and inelastic fibers the steps comprising forming a plurality of separated flat sheets of inelastic filaments and continuous elastic filaments, tensioning said sheets of elastic filaments to stretch said filaments a predetermined amount beyond their normal relaxed length, combining said sheets of elastic and inelastic filaments in layered relationship to form a composite web wherein said tensioned elastic filaments lie between adjacent sheets of said inelastic filaments, and thereafter feeding said composite web to fracturing means whereby said filaments are cut to staple lengths.

2. The method of claim 1 wherein said elastic filaments are stretched an amount from about 5% to about 15% greater than their relaxed length.

3. The method of claim 2 wherein said composite web is comprised of from. about 3% to about 50% by Weight of said elastic filaments.

4. The method of claim 2 wherein said elastic filaments are subjected to at least one cycle of stretching to from about two to five times their original length and relaxing after being formed into a flat sheet.

5. In a method of converting continuous elastic filaments and inelastic filaments into a sliver of intermingled staple fibers, the preliminary steps comprising forming a plurality of separated fiat sheets of continuous elastic filaments and inelastic filaments, tensioning said sheets of elastic filaments to extend said filaments a predetermined amount beyond their normal relaxed length, combining said sheets of elastic and inelastic filaments in layered relationship to form a composite web wherein said tensioned elastic filaments lie between said sheets of inelastic filaments, and thereafter feeding said composite web to fracturing means whereby said filaments are cut to staple lengths.

6. The method of claim 5 wherein said elastic filaments are extended an amount from about 5% to about 15% greater than their relaxed length.

7. The method of claim 6 wherein said composite web is comprised of from about 3% to about 50% by weight of said elastic filaments.

8. The method of claim 6 wherein said elastic filaments are subjected to at least one cycle of stretching to from about two to five times their original length and relaxing after being formed into a flat sheet.

No references cited. 

5. IN A METHOD OF CONVERTING CONTINUOUS ELASTIC FILAMENTS AND INELASTIC FILAMENTS INTO A SLIVER OF INTERMINGLED STAPLE FIBERS, THE PRELIMINARY STEPS COMPRISING FORMING A PLURALITY OF SEPARATED FLAT SHEETS OF CONTINUOUS ELASTIC FILAMENTS AND INELASTIC FILAMENTS, TENSIONING SAID SHEETS OF ELASTIC FILAMENTS TO EXTEND SAID FILAMENTS A PREDETERMINED AMOUNT BEYOND THEIR NORMAL RELAXED LENGTH, COMBINING SAID SHEETS OF ELASTIC AND INELASTIC FILAMENTS IN LAYERED RELATIONSHIP TO FORM A COMPOSITE WEB WHEREIN SAID TENSIONED ELASTIC FILAMENTS LIE BETWEEN SAID SHEETS OF INELASTIC FILAMENTS, AND THEREAFTER FEEDING SAID COMPOSITE WEB TO FRACTURING MEANS WHEREBY SAID FILAMENTS ARE CUT TO STAPLE LENGTHS. 